The invention relates to a current generator for delivering a reference current having a value which is proportional to the absolute temperature comprising an output terminal for delivering the current; a first and a second supply terminal for receiving a supply voltage; a first bipolar transistor having a collector coupled to the first supply terminal, a base, and an emitter; a second bipolar transistor having a collector coupled to the first supply terminal, a base, and an emitter; a first current source coupled in between the second supply terminal and the emitter of the first bipolar transistor; and a second current source coupled in between the second supply terminal and the emitter of the second bipolar transistor.
Such a current generator is known from the publication: "Micropower CMOS Temperature Sensor with Digital Output", IEEE Journal of Solid-State Circuits, Vol. 31, no. 7, July 1996, pages 933-937. In the known current generator the first and the second current sources are formed by respectively first and second PMOS-transistors of which theirs sources are coupled to the second supply terminal. A drain of the first PMOS-transistor is coupled to the emitter of the first bipolar transistor. A resistor is coupled in between a drain of the second PMOS-transistor and the emitter of the second bipolar transistor. The bases of the first and the second bipolar transistors are coupled to the first supply terminal. An operational amplifier is coupled with an inverting input to the drain of the first PMOS-transistor, with a non-inverting input to the drain of the second PMOS-transistor, and with an output to gates of the first and second PMOS-transistors. The operational amplifier controls a control voltage at the gates of the first and second PMOS-transistors in such a manner that the voltage difference between the drains of the first and the second PMOS-transistors is virtually equal to zero. By appropriate dimensioning of the components the voltage across the resistor is proportional to the absolute temperature. Also the currents flowing through the first and the second PMOS-transistors are proportional to the absolute temperature. In the known current generator a reference current which is proportional to the absolute temperature can be generated by the addition of a third PMOS-transistor of which its gate and source are connected to respectively the gates and sources of the first and second PMOS-transistors. The reference current can then be taken from the drain of the third PMOS-transistor.
Since reference currents are very often necessary in electronic circuits there is a need for alternative solutions.